This invention relates to instrumentation for measuring the vertical displacement from a reference point.
Instrumentation providing a precise measurement of small vertical displacements of a remote point from a reference point is particularly useful for the static deflection measurement of bridges, buildings and the like. Alternative uses include tunneling navigation, ship construction and soil settlement.
In the prior art, there are three principal classes of instruments for providing such measurements. The first, based on a water-tube, utilizes an elongated u-shaped tube having water or an equivalent fluid therein. Using such an instrument, one end of the tube is positioned with the fluid level therein at local reference point and the other (remote) end is positioned at the desired remote point. A graticule marking on the tube at the remote end may be used in conjunction with the fluid level at that end to provide a measure of the vertical displacement of that remote end of the tube from the local reference point of the reference end of the tube. However, such water tube based instrumentation depends on fluid flow within the tube and is also very sensitive to variations in surface tension of the fluid. Furthermore, dynamic instability and thermal error also contribute significantly to the cumulative error in such instrumentation.
A second class of instruments known in the art utilizes transit survey and other optical techniques. However, this class of instrumentation requires substantial care and set-up time, and further requires an optically transparent medium in order to accommodate the line of sight measurements. Furthermore, such equipment is relatively inaccurate over large distances.
A third class of instrumentation known in the art utilizes stain gauge techniques, and is principally used in the static deflection measurement of bridges and buildings. However, such instrumentation measures only local strain deformation at the point of strain sensor installation. In order to get a continuous range of strain measurements, an impractically large number of sensors is required. Furthermore, such sensors as presently known in the art are subject to significant long term drift, which in turn affects the accuracy of the resultant measurement.
Accordingly, it is an object of the present invention to provide an apparatus for measuring vertical displacement between a remote point and a reference point which is relatively accurate.
A further object is to provide an apparatus for vertical displacement measurement which is operative where line-of-sight is obscured.
Still another object of the present invention is to provide a vertical displacement measurement apparatus which is relatively independent of temperature.
Still another object of the present invention is to provide a vertical displacement measuring apparatus which is relatively independent of pressure.
Yet another object of the present invention is to provide vertical displacement measurement apparatus which is relatively independent of variation in environmental parameters affecting fluid flow.